Rennell Island

• Category: Marine and Oceanic Biomes
• Geographic Location: Pacific Ocean
• Summary: Home to one of the world’s largest coral atolls, and incorporating the largest Pacific-island lake, Rennell Island supports a variety of distinct species of flora and fauna.

Rennell Island is the main island of the two islands that comprise the Rennell and Bellona Province of the Solomon Islands. Known locally as Mugaba, Rennell Island has a land area of some 250 square miles (647 square kilometers). Considered one of the world’s largest raised coral atoll, Rennell is approximately 50 miles (80 kilometers) long and 9 miles (14 kilometers) wide, with a population of about 3,000 people, most of whom are of Polynesian descent. Renbelian and English are spoken, as well as a dialect known as Pigen.

The island is home to the largest insular lake in the Pacific region, Lake Tegano, which is listed as a World Heritage Site by the United Nations Educational, Scientific, and Cultural Organization (UNESCO).

Rennell has a tropical climate; temperatures average between 73 and 84 degrees Fahrenheit (23 and 28 Celsius) year round, with rainfall totaling approximately 157 inches (400 centimeters) annually. The island lies within the cyclone path, and cyclones have hit the island in 2019 and 2020. During Cyclone Oma in 2019, a bunk carrier carrying 700 tonnes of oil, ran aground and spilled 300 tonnes of oil into the bay. Drinking water became contaminated and people were unable to fish. Children suffered skin and eye infections. The damage caused by these environmental disasters lingered for several years.

Human Influence

Rennell Island was first settled sometime before 1400 CE, when clansmen from Wallis Island (Uvea) crossed the Pacific. The United Kingdom established a protectorate over the Solomon Islands, including Rennell, in 1893, which existed until self-governance was declared in 1979. Today, subsistence farming takes place on Rennell Island, with the major crops including sweet potatoes, slippery cabbage, and taro.

In 1933, explorer and amateur botanist Charles Templeton Crocker visited Rennell, in a trek known as the Templeton Crocker Expedition that resulted in a series of short reports on seaweed, fish, reptiles, and amphibians endemic (found only here) to the island, including a new species of sea snake. Other expeditions to survey the island and chart fauna and flora species occurred over the years, resulting in reports that concluded that the coral reefs of the Solomon Islands, including Rennell Island, were less spectacular than those in other locations. The reports added that these islands lacked the luxuriance of the Great Barrier Reef in the Coral Sea off Australia.

The poverty of Rennell Island’s coral reef was viewed as relative to the area’s geologically recent elevation, and its steep and sometimes vertical gradients that discouraged the growth of coral and vegetation. The coral collections of Rennell Island have all, or virtually all, Indo-Pacific hermatypic scleractinians (zooxanthellate algae that support hard corals) present. Despite Crocker’s pronouncements, Rennell Island is now considered one of the best global examples of reef-coral genetic diversity.

Biodiversity

Rennell Island is covered in dense forest with a canopy averaging 65 feet (20 meters) tall. Local flora includes low scrub forest on the karst ridge, tall forest in the interior, and beach flora along Lake Tegano. The lake’s vegetation features 312 species of diatoms and algae, including some endemic species.

Throughout the Solomon Islands, more than 700 species of algae are present, but no comprehensive collection has been made of marine algae near Rennell Island. Seaweed diversity near Rennell is low compared to other places. Seagrass beds, which help reduce surface erosion and bind sediments, are typically inshore of coral reefs. Although no comprehensive list of seagrasses near Rennell has been compiled, at least seven species have been noted, including Cymdocea, Enhalus, Halodule, Halophila, and Syringodium.

More than twenty-six species of mangrove are found near Rennell Island, representing more than 40 percent of the world’s mangrove species. Mangroves protect coral reefs by removing and binding sediment that comes down from rivers. They also help recycle nutrients within lagoons, and shelter some bait-fish species that migrate between lagoons and coral reefs. Baitfish, which are captured for use in tuna fishing, are an important part of the Rennell Island economy. More than 200 species of marine fish have been identified near Rennell Island, many of which are eaten by local residents.

Rennell and Bellona are home to several endemic bird species, including the Rennell starling (Aplonis insularis), bare-eyed white-eye (Zosterops superciliosus), Rennell shrikebill (Clytorhynchus hamlini), and the Rennell fantail (Rhipidura rennelliana). The Solomons white ibis (Threskiornis molucca pygmaeus) is a dwarf subspecies of the Australian white ibis that is endemic to the islands.

Rennell Island also is home to twenty-five species of ants, twenty-seven species of land snails, and eleven species of bats, including the Rennell flying fox (Pteropusrennelli), which is unique to the island. Coconut crabs (Birgus latro), the world's largest terrestrial arthropod, also live on the island.

Lake Tegano, at 18 miles (29 kilometers) long and 6 miles (10 kilometers) wide, comprises nearly 18 percent of the total area of Rennell Island. With a maximum depth of about 145 feet (44 meters), Lake Tegano is a mixture of brackish, fresh, and salt water. Home to eels, water snakes, and birds, Lake Tegano sits in a central basin on the island that once served as the lagoon.

Environmental Concerns

The sparse population here helped keep the natural vegetation mostly intact for decades, and there were no serious invasive species of animals or plants. However, climate change and environmental disasters began to impact Lake Tegano via rising water levels, increased cyclone frequency, oil spills, logging, and more persistent water salinity. Climate change also adversely affects plant growth in low-lying areas, which reduces taro and coconut harvests, both staple foods for the islanders. In January 2024, a Participatory Rapid Appraisal (PRA) assessment found the island was experiencing significant environmental threats. Invasive black rats were destroying crops. Water quality and quantity continually decreased, along with nearly all marine resources. Efforts to preserve the island's biodiversity and integrate new farming practices aimed to address these issues.

Bibliography

Alsford, Niki J. P. Pacific Voices and Climate Change. Palgrave Macmillan, 2022.

"East Rennell." UNESCO World Heritage Centre, whc.unesco.org/en/list/854. Accessed 20 Oct. 2024.

Gillespie, A., and W. C. G. Burns, editors. Climate Change in the South Pacific: Impacts and Responses in Australia, New Zealand, and Small Island States. Kluwer, 2010.

McKibben, B. Deep Economy: Economics As If the World Mattered. Oneworld Publications, 2007.

Puia, Mike. "'They Failed Us': How Mining and Logging Devastated a Pacific Island in a Decade." The Guardian, 30 May 2021, www.theguardian.com/world/2021/may/31/they-failed-us-how-mining-and-logging-devastated-a-pacific-island-in-a-decade. Accessed 30 Aug. 2022.

Wolff, T., and Edred John Henry Corner. “The Fauna of Rennell and Bellona, Solomon Islands.” Philosophical Transactions of the Royal Society of London, Biological Sciences, vol. 255, no. 800, 1969, pp. 321–43, doi.org/10.1098/rstb.1969.0014. Accessed 20 Oct. 2024.